The area (or the absorbance measured at the constant signal) and the absorbance measured at the minimum of the peak can be used as measures corresponding to the phosphate and silicate concentrations, respectively. The time of the peak registration is about 3 min. Two-component calibration with the use of four standard solutions of the phosphate/silicate concentrations established in accordance with 22 factorial design was applied. Phosphate and silicate can be determined within the concentration ranges of 0.20–15.00 and 0.20–20.00 mg L−1, with precision less than 2.7 and 0.9% (RSD), respectively and accuracy better than 6.2% (RE). The detection limit is 0.054 and 0.092 mg L−1 for phosphate and silicate, respectively. The method was applied to determination of the analytes in certified reference materials of groundwater, wastewater, and river water giving results consistent with the certified values.